Rear end roar

I have a 1991 Infiniti Q45 that has had all bearings, motor mounts, transmission mounts etc replaced. It has a new drive shaft and the rear end has been taken apart and checked. The transmission has also been rebuilt.

The problem is there is a roar in the rear end at between 38 to 43 mph. The roar only shows up either in 4th gear or in neutral. Over 45 the roar goes away. (It is loud enough that you would still hear it at 60 even with road and wind noise.)

Everything has been check that we can think of. Hopefully someone will have a suggestion of what else to try.

Tire noise perhaps? Rotate the tires front to rear and see if the noise moves to the front.

Are you certain that the roar is in the rear end? It might be helful to have the shop put it up on a frame lift and then run the car and listen with a stethascope. The problem could be a bearing in the transmission the sounds as though it is in the rear end. It could also be in the differential.

Thanks for the suggestion. We tried putting different wheels and tires on the car to no avail.

Almost certain that it is the rear end but who knows. We have had it up on the lift a couple times but even listening with a stethascope has not helped. The noise only shows up when there is a load on the wheels.

what bearings?

motor mounts and rear end noise,not feesable.,nor logical,hmmmmm!

how has the rear been checked(in detail?) please!

tranny been checked too?

need alot more info to help you at all.

you are SURE it makes the noise in 4th AND N and nothing else? that sounds like a rear end, differential rear axle/bearing issue.

you state the rear end was ‘checked’ sounds like it needs more than a check. and the bearings/ axles has that been checked on the rear too?

The reason I asked is that I had a similar problem with a 1965 Rambler. It had this noise and was under warranty. The service department at the dealer thought that the noise was in the rear end and rebuilt the differential. This did no good. The problem was a bearing in the transmission (manual transmission). These noises can be deceptive.

My experience has been that with rear ends, bearings are not checked, just replaced. Expensive but that is how goes.

First I am not a mechanic but this is what I have been told has been replaced. Wheel bearings, all bearings that are in the rearend(my understanding), new drive shaft(fixed a vibration), transmission mounts(eliminated another small vibration), motor mounts(removed last of vibration), new struts all around, rear end has been taken apart twice to make sure it is within factory tolerance, I believe the mechanic called it a chassis mount for the rear end - it was replaced. The car runs as smooth as it did when new just has a roar at the listed speeds.

doh, i didn;t think to say it that way! that was put clearer.

if you are going to the trouble to ‘check’ the rear end, why not DO the bearing replacement anyway?

doh,glad you agree!!!